Republican Senator Pat Toomey’s vote will be in high demand Monday, Nov. 4, as it could be the key to passing a bill.

The senate will be voting that evening on a bill to ban workplace discrimination based on sexual orientation or gender identity, the Employment Non-Discrimination Act, also known as ENDA. The bill is backed by at least four Republicans so far, but it does still need one more senator on its side to clear some procedural hurdles.

The first openly gay Pennsylvania Representative, Democrat Brian Sims of Philadelphia, wrote an open letter to Toomey on Friday, Nov. 1, urging him to support the bill.

A spokesperson said Friday that Senator Toomey is still undecided on his vote.